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Table 5. Percent change in mean-daily streamflow during the period when aerial video and YOY Colorado squawfish data were collected, Greece and Colorado rivers, 1989 to 1991. Percent Change in Mean-Daily Streamflow ------------------------ Reach 1 Reach 2 Reach 3 Reach 4 Video Video Video Video and Video and Video and Video and Video Year ISMP` Only" ISMP Only ISMP Only ISMP Only 1989 -7% -3% +9% 0% +22% 0% +22% +22% 1990 +60% -28% -21% 0% +67% 0% +51% +19% 1991 -3% -3% -3% 0% +2% 0% -11% _6% `Percent change during the pen including both video collection an ISMP sampling. 'Percent change during the period including only video collection. Backwater area and streamflow showed negative, linear relationships in reaches 1, 3, and 4, but essentially no relationship in Reach 2 (Figure 3). Pucherelli and Clark (1989) reported that flows between 1,000 and 1,800 CFS maximized backwater habitat in the upper Green River (Reach 4). This study found the greatest number and area of backwaters at the lower end of that range for the same reach (measured from one year to the next; Table 6). There was considerable variation in backwater surface area with relatively small fluctuations in average streamflow in some reaches. For example, a 17% increase in streamflow in Reach 2 resulted in a 120% increase in surface area of backwaters and a 16% decrease in streamflow in Reach 3 resulted in a 133% increase in backwater surface area (Table 6). Based upon regression equations developed from data in Table 6 and using stream flow changes indicated in Tables 3 and 4, backwater area could have changed substantially during ISMP sampling (Reach 1: 89-4 %, 90-25 %, 91-5 %; Reach 2: not calculated, poor correlation; Reach 3: 89-14%, 90-35%, 91-5%; Reach 4: 89-15%, 90-26%, 91-15%; Appendix Table A2). These numbers over state the problem because at least some ISMP seining occurred on the same day as video collection and other seining would have occurred at streamflows between the extremes represented above. Nonetheless, a high percentage of seining was done at flows different than those used to measure backwater area. Another potential source of error involves apparent differences in backwater identification between ISMP investigators and video interpreters. The most obvious difference occurred in Reach 3 during 1991 when investigators did not take any samples in a 10-mile section of river--presumably because no backwaters meeting the minimum ISMP criteria (> 30 m2 in surface area and > 30 cm deep at its maximum depth) were found. Although no samples were taken, six backwaters > 30 m2 were identified from the video 10 1 1